Retractable drill



April 11, 19 J. E. ECKEL ETAL RETRACTABLE DRILL 3 Sheets-Sheet 2 Filed22. 1957 John M Comp John E Ecke| Inventors By W Anorney April 11, 19 J.E. ECKEL ETAL RETRACTABLE DRILL 3 Sheets-Sheet 3 Filed Aug. 22, 1957John M. Comp J h Eckel Inventors y a Afforney United States PatentRETRACTABLE DRILL John Edward Eckel and John M. Camp, 'lhlsa, 0kla.,-

assignors, by mesne assignments, to Jersey Production Research CompanyFiled Aug. 22, 1957, Ser. No. 679,652

12 Claims. (Cl. 175-232) This invention pertains generally to boreholedrilling and more particularly to an improved type of retractable drilland bit. The invention especially pertains to a form of retractabledrill which is particularly flexible in that it is suitable for drillingnot only large-diameter holes but also small-diameter ones.

A very large portion of the expenditures that are made each year by thepetroleum industry in its quest for oil is concerned with drillingboreholes. In view of this fact, there has been a continuing effort onthe part of the petroleum industry to reduce the high costs that areassociated with drilling. Much progress has been made over the years inthis direction, but there is still much room for improvement. Improveddrill bits, less expensive rig designs, improved drilling fluids, etc.,have contributed much to less expensive and more eflicient drilling; butthese gains are being ofiset to a considerable degree by the increasingdifliculty in finding and producing oil. For example, it is becomingnecessary to drill to progressively greater depths in order to find newoil reserves; and these greater depths are directly reflected in greaterdrilling expenses.

Rotary drilling is the most generally employed system of drilling in usetoday; and, accordingly, most eiforts at improving drilling efi'iciencyhave been directed toward this particular technique. In this system ofdrilling, a multi-cutterbit is attached to the lower end of a string ofpipe; and the entire assembly is rotated so as to crush and pulverizethe earth underlying the bit. A drilling fluid in the form of drillingmud, water, air, or

the like is circulated past the cutters via the drill pipe and sub, anda packer seals the annulus between the mandrel and the sub.

Another attractive form of retractable drill is set forth in US. PatentNo. 2,771,275-J. E. Ortloif; and still another type is shown in US.2,208,457W. G. Hurley. All of these drills vary in material respects,but they still resemble one another in that each one uses a mandrelcarrying a plurality of cutters which enters and cooperates with a subto form an integral drill bit which is retractable in character. A

In spite of their obvious advantages, the adoption of retractable drillsby the petroleum industry has been relatively slow-partially because ofcertain mechanical limitations, and partially because of recent trendsin the drilling art. For example, mechanical limitations of presentlyknown retractable drills have been major deterrents in their applicationto the drilling technique popularly known as slim-hole drilling.Slim-hole drilling-as its name implies-consists essentially in drillingwell completion.

the annulus between the pipe and the borehole so as to flush cuttingsfrom the hole.

A serious and expensive disadvantage of the rotary drilling techniquelies in the fact that the entire length of drill pipe must be removedfrom a borehole in order to replace a worn-out drill bit. This is anoperation which necessarily requires considerable time and money; andrepeated efforts have been made to avoid it. One of the most attractivesolutions to this problem is a recently developed retractable drillWhose bit can be lowered through a well pipe, assembled and expanded inposition at the bottom of the pipe, and thereafter retracted andwithdrawn from the pipe as desired. A particularly efiective drill ofthis character is described in United States Patent No. 2,764,388-1. M.Camp. This particular drill makes use of a special sub which is attachedto the lower end of a drill string and which is adapted to receive amandrel or body member carrying a plurality of cutter elements. Suitableinterlocking or interengaging means cooperate with the sub and themandrel to assemble the elements as an integral bit at the lower end ofthe sub. No particular orientation of the mandrel or cutter elementsrelative to the sub is required to expand or retract the bit.Retractable interengaging or locking means hold the mandrel within the-While the advantages of both slim-hole drilling and retractable drillshave heretofore been recognized in the art, the two techniques have beenincompatible for the reason that retractable drills have heretofore notbeen available or feasible in small sizes. Small-diameter retractabledrills tend to have shorter lives than conventional non-retractable bitsof equivalent size; and they are also quite sensitive to variations inhole size. Thus, in some instances where a retractable bit has beenremoved from a borehole because of wear, diificulty has been experiencedin replacing the bit with a new member by virtue of the fact that thenew bit-being somewhat larger than the old bitcould not be sufiicientlyexpanded within the narrow hole cut by the previous bit.

Another difiiculty that has beset retractable drillsand especiallysmall-diameter drillshas centered about the bearings that are used withconical-type cutters. Thus, in spite of the fact that both slim-holedrilling and retractable drills have been known to possess markedadvantages, no satisfactory solution has been advanced or suggested todate for combining these two ideas.

Accordingly, it is an object of the present invention to improve uponthe structure and use of retractable drills and bits. It is a furtherobject of the invention to render retractable drills and bits morepractical and attractive for general use, and especially for use inslim-hole drilling. It is an especial object of the invention toovercome the difiiculties that have been experienced with retractabledrills and bits resulting from variations in drill hole size.

It is a general object of the invention to reduce the costs of drillingboreholes so as to render this technique more satisfactory, not only forpetroleum production purposes, but also for straight explorationpurposes. Numerous advances in geological and geophysical research havebeen made in recent years to aid in the discovery of new oil reserves;but the only completely certain method of establishing the existence ofa subterranean oil depositlowing description, are realized by the use ofan improved type of drilling design.

The present invention, in essence, relates to improvements in the typesof retractable drills and bits generally described in the aforementionedpatents. Thus, like those patents, it concerns a drill which includes amandrel and a tubular member or drive sub. The sub is attachable to thelower end of a string or well pipe, and it is adapted to receive themandrel. The latter member, which carries a plurality of bit or cutterelements, is adapted to be manipulated as by means of a wire line withinthe well pipe; and it is further adapted to fit within and engage withthe drive sub in a retractable manner. Each bit element is suspendedfrom the mandrel by means of a support member which includes at itsupper end a latching device, dog, or equivalent means for alternatelyengaging sets of locking means disposed within the mandrel and the drivesub. When the cutter support members are locked to the mandrel, thecutter elements are preferably arranged in a vertically spaced, nestedrelationship so as to occupy a minimum lateral dimension when beingmanipulated within a drill string. Alternately, when the cutter supportmembers are locked to the drive sub, the cutter or bit elementsare'positioned on the same lateral plane and immediately below and inengagement with the lower portion of the drive sub. Furthermore, whenthe locking devices have engaged the cutter support members with thedrive sub, the mandrel is adapted to move downward against the cutterelements and to wedge them into engagement with the lower end of thesub.

In this invention, each cutter or bit element as well as the lower endor surface of the mandrel is provided with an abrasive-type cuttingsurface. When expanded into drilling position, the cutting surfacescombine to form an integral cutting surface which drills against theentire bottom of a borehole. A central or main drillingfluid passagewayis provided throughout the length of the mandrel, and branch passagewaysconnecting with the central mandrel passageway and extending througheach cutter element are provided for the circulation of a drillingfluid. Packing means are provided on the mandrel to seal the annulusbetween the mandrel and the sub so as to require a drilling fluid topass down through the mandrel and thence through the annulus between thedrill string and the wall of the borehole.

The bit elements may rely upon sheer frictional forces to maintain themin positive engagement with the drive sub; but they and the sub arepreferably equipped with matching splines or other positive-typeinterengaging means so that a completely positive driving arrangementmay be assured.

In a preferred version of the invention, the lower end of the sub andeach bit element is designed so as to define a movable jointtherebetween which enables the ele ments to move in a longitudinal(i.e., normally vertical) plane when in engagement with the drive sub.Thus, as the mandrel travels downward within the sub and urges the bitelements radially outward from the mandrel, the elements are capable ofa somewhat pendulum-like movement as they swing around the end of thesub into drilling position. This articulated action of the bit elementsenables them to be held in a firm manner between the mandrel and thedrive sub even though they may not fully expand into their normaldrilling position.

Once the mandrel has entered within the drive sub and the cutter supportmembers have engaged the drive sub, the mandrel is maintained within thedrive sub through the use of suitable interengaging means of aretractable type. A lost-motion device or equivalent means is preferablyincluded in the apparatus so that the mandrel is capable of longitudinalmovement within the drive sub after the interengaging means has lockedthe mandrel within the drive sub. The lost motion is desirable from dthe standpoint of setting a packer or enabling the mandrel to expand thebit elements into drilling position.

In a preferred version of the invention, the drilling-fluid passagewayin each bit element is constructed so as to be in fluid communicationwith the central drilling-fluid passageway in the mandrel only when themandrel and the bit elements are in their fully expanded normal drillingposition. Otherwise, the drilling fluid fiows in a restricted mannersolely through the mandrel, with the result that a fluid force isexerted against the mandrel, continually urging the mandrel into itsnormal drilling position.

In a still further preferred version of the invention, each bit elementis'pivotally mounted on its support member so that expansion andretraction of the element is facilitated.

Having generally outlined the major components and features of thepresent invention, attention is now directed to the figures for a morecomplete and clearer understanding of the invention. The figuresillustrate an apparatus constituting a preferred embodiment of theinvention which is contemplated to be the best mode for practicing theinvention.

Figure 1 illustrates an apparatus of the invention in vertical crosssection, as the apparatus appears with its bit elements in a retractedposition for movement within a string of well pipe. Figure 1(a)illustrates a lower portion of the apparatus and Figure 1(b) an upperportion thereof.

Figure 2 illustrates the apparatus of Figure 1, again in cross section,as the apparatus appears with its bit elements and mandrel completelyexpanded into normal drilling position.

Figure 3 is a section view taken along the line III-III of Figure 2.

Figure 4 is a section view taken along the line IV--IV of Figure 2.

Figure 5 is a section view taken along the line V--V of Figure 2.

Figure 6 is a bottom view of the apparatus shown in Figure 2 depictingthe orientation of the mandrel and the cutter elements when in a fullyexpanded drilling position.

Figure 7 is a section view of the same apparatus shown in Figure 1, butwith the bit elements and mandrel incompletely expanded.

Figure 8 is a partially sectioned view of a tool suitable for expandingor retracting the apparatus of Figures 1-7.

Figure 9 is a bottom view similar to Figure 6 but showing the fullyexpanded arrangement of a bit comprising a mandrel and three bitelements.

In referring to the figures, it will be observed that the same legendsare used throughout the figures to identify identical parts orcomponents. Thus, the major structural components shown in the variousfigures include 1 of a string of drill pipe; and it preferably has aninner diameter corresponding to the inner diameter of the pipe. Theouter diameter of the sub may be somewhat larger than the drill pipe inorder to provide the sub with added strength and rigidity. I

Near the upper end and interiorly of drive sub 10 is a circumferentialgroove or recess 16 which possesses a downward-facing upper shoulder 21and a tapered uprecess 15 within drive sub is positioned at a pointintermediate the ends of the sub. This recess possesses an upward-facinglower shoulder 23 and a tapered downward-facing upper shoulder 24. Theextreme lower end of the drive sub terminates in an inwardly tapered anddownward-facing shoulder 29, the angle of taper being preselected in amanner to be described later in this discussion.

Spaced slightly above shoulder 29 is a recess 17 which includes a curvedspline section 26 comprising a plurality of longitudinally disposed andarcually spaced splines 25. As will be brought out later in thisdescription, these splines coact with mating splines on each one of thebit elements 12 to effect a positive drive relationship between the suband the bit elements. The upper end of recess 17 is preferably taperedso that the splines on the bit elements freely engage the splines on thesub. The spline section 26 is grooved or curved to define a movablejoint or bearing surface with a mating portion of each cutter element.Conveniently, the groove 26 is rounded or circular in profile for thispurpose.

Adapted to fit within drill sub 10 is mandrel 11 which carries with itbit elements 12, packer 18, lower retractable interengaging or latchingdevices 14, upper interengaging means or latches 19, sleeve 20, andsleeve valve 27. A central passageway 28 extends longitudinallythroughout the mandrel and provides means for conveying drilling mud orother drilling fluid from the interior of the string of well pipe to thevarious elements of the bit. The lower end of this passageway terminatespreferably in a jet 30 adapted to direct drilling fluid verticallydownward from the mandrel. A plurality of branch passageways 31interconnect the central passageway above the jet with ports 32 insleeve valve 27 and fluid passageways 33 in each bit element 12.

The lower end of the mandrel 11 is covered with an abrasive-type cuttingsurface (preferably diamonds); and radially extending grooves 35 arepreferably provided to conduct drilling fiuid from the jet 30 towardadjoining surfaces of the cutter elements 12. It has been found inpractice that drill cuttings tends to collect in the regions between thebit elements with adverse drilling resuits, and this condition isgreatly relieved by the use of these grooves. It will be recognized, ofcourse, that other passageway and groove configurations may be used asdesired.

Immediately above the lower end of the mandrel 11 is a peripheral recess36 which acts somewhat as a valve guide or seat for the sleeve valve 27.This, recess is somewhat longer than the valve in order that a degree oflongitudinal movement of the valve along the mandrel is possible.

The outer surface of the valve 27as well as the adjoining surface of themandrel 11-is tapered to enable the mandrel to apply a wedging actionagainst the inner surface portions of the bit elements 12 when the bitelements are expanded into a drilling position and placed in engagementwtih the drive sub 10. Additionally, the ports 32 in the valve 27 arepositoned so that the ports are: (1) in direct alignment with the branchpassageways 31 and the bit element passageways 33 when the valve is inits uppermost longitudinal position and the bit elements and mandrel arein a fully expanded drilling position, and (2) out of alignment with thepassageways 31 and 33 when the valve 27 is in a position other than itsupper most position and the bit elements are in an so that it isnormally urged outward from the holder. Each dog is also provided with alower shoulder adapted to engage the shoulder 23 of the drive sub andwith a tapered upper shoulder matching the shoulder 24 of the drive sub.Furthermore, each dog is made of a suflicient length and is preferablyrounded off so that it may move freely within a string of well pipewithout obstruction by the pipe joints.

Secured to the lower ends of the latch assemblies 41 and integraltherewith are elongated bit element supports 13. The lower end of eachsupport is attached to an upper portion of a bit element 12preferably ina pivotal or otherwise articulated manner. Thus, as illustrated in thedrawing, each support 13 is attached to its respective bit element bymeans of a pin 45. The connection between each support and each bitelement may be rigid if so desired, but the support must then besufficiently flexible to enable free movement of the bit elements to andfrom their drilling position.

Vertically spaced dog recesses 46 and 47 are positioned alongthe'mandrel 11, each recess being in alignment with one of the groovesor slots 40. Each such recess is adapted to receive one of the dogs 'orlocking devices 14 when the bit elements are in a retracted position formanipulation within a string of well pipe.

At this point, it will be noted that the bit elements 12 in a retractedposition should occupy a smaller lateral cross-section area than they dowhen in an expanded drilling position-otherwise, it would be difficultto manipulate the mandrel and its associated bit elements convenientlyto and from a drilling position. This condition is most conveniently metby simply spacing the recesses 46 and 47 along the length of the mandrel11 and by varying the lengths of the support members 13. Thus, in aretracted condition, the bit elements 12 are staggered vertically in anested relationship; while, in an expanded drilling position, the bitelements are all On the same lateral plane.

At this point, it will further be noted that the apparatus shown in thedrawing is depicted as possessing two bit elements. An apparatuswithmerely two bit elements has been chosen to lilustrate and explainthe invention, since the description of an apparatus of this type isrelatively straightforward and readily understood. It should be pointedout, however, that an apparatus employing more than two cutters orelementspreferably three cutters-is actually more desirable for thepurposes of the invention. When using three bit elements, the elementsand their respective dogs and supports are spaced apart around themandrel. When two bit elements are employed, the spacing is as shown inthe drawing. A three-element or cutter bit is shown in Figure 9.

Positioned above the dog holders 42 and separated therefrom, preferablyas by means of a spring 50, is a packer 18 which comprises an elasticdeformable sleeve 51, upper and lower rings 52 and 53, respectively, andbushing 54. The bushing 54 is the component of the packer which actuallyrests upon the spring 50 and is slidable longitudinally along themandrel 11. Sealing means in the form of packing or the like 55 ispreferably provided on the inner surface of bushing 54 in order toeffect a fluid-tight seal against the mandrel.

The lower end of the sleeve 51 is secured between the bushing 54 andring 53, and the upper end of the sleeve is similarly secured betweenring 52 and the lower end of sleeve 20. The sleeve-preferably made ofnatural or synthetic rubberis preferably pleated in the manner shown toresemble a bellows or accordion-like member. Conventional sleeve-typepackers may be used with the invention, but it has been found byexperience that a pleated-type packer such as just mentioned is far moreeffective in maintaining an effective fluid-tight seal. The sleeve in anunset condition should be less than the diameter of the well pipe anddrive sub in which the packer is to be manipulated. When set, however,the packer my d should be capable of expanding against and contactingthe inner wall surface of the drive sub.

The sleeve 20 and the upper packer ring 52 are conveniently threaded orotherwise adapted to be connected to one another. The bushing 54 and thelower ring 53 are similarly threaded or otherwise adapted to beassembled.

With further reference to the sleeve 51, it will be noted that only oneof the bellows elements in the sleeve preferably actually seals againstthe inner wall of the sub 10. Only one bellows element is required forthis purpose, the other bellows elements being present primarily toenable the sleeve 51 to be contracted longitudinally a substantialamount. A longitudinal groove or passageway 56 is preferably providedalong the upper portion of the mandrel 11, the purpose of this groovebeing to vent the inner portions of the bellows elements of the packersleeve -1. A similar groove 57 is provided to vent outer portions of thebellows elements of the packer sleeve. Any liquid entrapped within thebellows elements is therefore able to escape from the bellows elements,thereby enabling the packer to be set with relatively low loadings.

Sleeve 20 extends up beyond the end of the mandrel 11 and is providedwith ports 58 through which the upper dogs, latches, or equivalentinterengaging means 19 may pivot. Thus, in the drawing, both dogs 19 arepivotally mounted on pins 60; and the pins in turn are mounted withinthe sleeve 20. Each dog is provided with an upper shoulder adapted toengage the shoulder 21 of the sub 10, and the dogs are further providedwith tapered lower shoulders. The upper ends of the dogs 19 are furtherprovided with downward-facing shoulders 61 which are adapted to engagethe spearhead of a tool for raising or lowering the mandrel and itsassociated components. A suitable such tool is one shown in Figure 8,the spearhead of this tool being identified by the legend 74.

It will be noted that the upper dogs or latches 19 are normally urgedoutward from the mandrel as by means of suitable springs or otherresilient elements not shown. The uppermost portion of each latch or dog19 terminates in a tapered section 62, the purpose of this section beingto cooperate with a suitable tool so as to urge the dogs inward when itis desired to retract the drill and manipulate it within a drill stringor the drive sub. As mentioned earlier, a suitable tool for this purposeis shown in Figure 8 and includes sinker bar 80, upper spearhead 81,stem 82, spring'83, retracting sleeve 84, the lower spearhead 74, andpin 85. Sleeve 84 is slidably movable along stem 82 and is normallyurged downward or away from the sinker bar 80 by means of spring 83. Thetool is illustrated in Figure 8 with the spring 83 in its expandedposition, this being the condition of 16 spring when the tool isemployed to retract the drill assembly. The pin 85 is not inserted inthe tool during this phase of operation. Lifting of the drill by thetool is actually effected when the inner shoulders 65 of the dogs 19engage the shoulders 66 located near the top of the mandrel.

When the tool in Figure 8 is used to lower a drill into a borehole,spring 83 is compressed; and pin 85 is inserted in the matching holes 86of the sleeve 84 and hole 87 of the stem 82. The pin thereby holds thespring in its compressed position. Sleeve 84 is provided with a conoalrecess at its lower end to enable the sleeve to retract dogs 19 bybearing down upon the shoulders d2. Upper spearhead 81 is attachable toa wire line or equivalent means for raising and lowering or otherwisemanipullating the retracting tool.

Referring next to the bit or cutter elements 12, it will first be notedthat the cutting surfaces of these elements are hard abrasive particles.Diamonds are preferred, but other materials such as carborundum,tungsten carbide, etc., may also be used if so desired. The cuttingsurface embraces the entire lower areal portion of each bit element aswell as a portion of the sidewall surface thereof.

a or Furthermore, areal configurations of the bit elements and the lowerportion of the mandrel are preselected so that the cutting surfacesgenerate a cutting action on the entire bottom of a borehole when thebit is in a fully expanded condition.

The interior surface of each bit element is tapered to receive the lowerportion of the mandrel 11, and the outer upper surface of each bitelement is similarly tapered to match the lowermost shoulder 29 of thesub 10. The upper outer surface of each bit element 12 is also profiledto mate with the splined portion 26 of the drive sub in a movablyarticulated manner as described earlier in this presentation. Thus,where the splined section of the drive sub has a curved or roundedprofile 26, the outer upper portion of each bit element is similarlysplined and contoured to move within this portion of the drive sub.

With respect to the tapered outer portion of each cutter element whichengages the shoulder 29 of the drive sub, it is preferred that a taperangle with a vertical of about 35 to 40 be used. It has been found thatangles within this range provide a uniquely advantageous distribution ofthrust and space for the expansion and retraction of the cutterelements.

Referring again to the splined portion of the drive sub and to thecorresponding splined portion of each cutter element, it will be notedthat sharp edges should be avoided with these portions in order that thesplines may readily engage and disengage.

In order that the cutter elements be fully capable of entering withinthe drive sub without requiring any substantial orientation, it isdesirable that a sulficient number of splines be used on the drive sub.It is further preferred that the number of splines in the sub be evenlydivisible by the number of bit telements. For example, sixty splineswould be suitable for use with bits containing anywhere from two to sixbit elements. It has been ascertained that engagement of the splines ofthe bit elements with the matching splines in the drill sub are greatlyfacilitated when this condition is observed.

Having thus described in some detail the various parts of the apparatusshown in the drawing, attention is now directed'toward the manner inwhich the apparatus is best operated. For this purpose, it will beassumed that the apparatus is first in a condition to be lowered withina string of drill pipe.

Referring to Figure l, the apparatus of the invention is thereillustrated in the condition required to enable it to be lowered withina string of drill pipe. The spear- .ead '74 of the lowering toolillustrated specifically in Figure 8 is engaged with the shoulders 61 ofthe upper intere-ngaging means or dogs 19, and the entire mandrel andbit assembly is suspended from the spearhead. The dogs are therebymaintained in a fully retracted condition; and, since the packer 18 isunder no compressive loading, it is also in a retracted condition. Thebit elements 12 are in a retracted, vertically nested condition, thelatch assembly 41 being secured to the mandrel 11 by virtue of dogs 14being positioned in recesses 46 and. 47. Sleeve valve 27 rests againstthe lower shoulder of the valve guide or recess 36, so that thepassageways 31 and the valve ports 32 are out of alignment. At thispoint, it should be noted that the sleeve valve 27 and the mandrel arepreferably splined, keyed, or otherwise adapted to be maintained inlongitudinal alignment with one another at all times.

When the mandrel and its associated parts are lowered within the drivesub, the following sequence of operations takes place. First, the lowerone of the two dogs 14 reaches groove 15, with the result that it popsout into the groove from its recess 46. Since the lower dog isautomatically clear of the mandrel when it engages groove 15, themandrel remains free to move vertically downward relative to this dogand the drive sub.

Simultaneously with the entry of the lower dog into 9 groove 15, lowerbit element associated with or suspended fromthe lower dog tends toexpand into a drilling position immediately below the lower end of thedrive sub. In other words, the tapered outer surface of the bit elementapproaches the shoulder 29 of the drive sub; and the curved splinedportion of the bit element tends to engage the curved splined portion ofthe drive sub.

Following engagement of the lower of the two bit elements with the drivesub, mandrel 11 continues vertically downward with its remaining dog andcutteri.e., the upper of the dogs 14 and the upper of the cutterelements 12. When the remaining dog reaches groove 15, it-like the firstdog-disengages itself from the mandrel and enters the groove.Simultaneously, its bit element tends to expand into a drilling positionradially opposite the first cutter. Then, mandrelll-being free of bothlocking dogs-continues to move downward relative to the drive sub andthe bit elements until its lower wedging surface bears against the innertapered surface of the bit elements. This action on the part of themandrel tends to wedge the cutters apart and to force them firmly intodrilling position within the drive sub. If the outer diameter of thebit-as defined by bit elementsis no greater than the diameter of theborehole, the mandrel and the bit elements assume the position shown inFigure 2. Furthermore, the sleeve valvedue to its tapered outersurfaceengages the inner tapered surface of the bit elements and ridesupwardly within the valve guide or recess 36. As a result of the sleevevalve action, the valve ports are in mutual alignment with the branchpassageways 31 and the bit element passage,- ways 33.

At this point, it is well to note that it is generally necessary toemploy a sinker bar or other equivalent means for applying a load on themandrel 11 which is sufficient to wedge the bit elements into theirdrilling position. As shown in Figure 8, a suitable sinker bar 80 may beincorporated directly as a component of the tool which is used to raiseand lower the drill assembly.

Once the bit elements have been wedged into their drilling position,expansion of the packer 18 is the next necessary step in the operatingsequence. To effect expansion of the packer, the sinker bar 84) ofFigure 8 exerts a downward thrust through spearhead 74 and the upper endof sleeve Iii-the thrust being sufiicient to drive the sleeve 20downward along with the attached upper packer ring 52 and the rubbersleeve 51. Since the lower end of the sleeve 51 is supported by thelower packer ring 53 and the bushing 54, and since the bushing and lowerring in turn are supported through spring 50 from the holders 42,longitudinal compression and radial expansion of the sleeve 51 results.Any liquid or pressure entrapped within the inner portions of thebellows elements of the sleeve 51 is relieved through the grooves 56 and57 in mandrel 11. The packer sleeve 51 forms a peripheral seal betweenthe mandrel and the inner wall surface of the drive sub. The degree ofcompression and the degree of sealing may be readily controlled by theamount of force which is applied by means of the sinker bar.

Concurrently with the setting of the packer, upper dogs or latches 19spring outwardly until they enter the groove or recess 16 in the drivesub. Since the spearhead 74 is hearing directly against the sleeve 20,it follows that the dogs 1& are free to expand and ride along the innersurface of a string of drill pipe and the drive sub until they reachthis groove or recess.

Once the dogs 19 have engaged the recess 16 and the packer has set, andthe bit components have expanded into drilling position, the drill isarranged as shown in Figure 2 and is ready for drilling. At this point,spea rhead 74 may be raised vertically from the apparatus and removedfrom the borehole, since the dogs 19 cannot escape or retract withoutthe application of a suitable tool as mentioned earlier.

' Actual drilling with the apparatus of Figure Zis' at tained bylowering the drive sub and the attached well pipe above the sub untilthe cutter elements (i.e., the assembled bit) reach the bottom of theborehole. Rotation of the bit, the drive sub, and the well pipe may beobtained conveniently by the use of conventional surface rotaryequipment; and loading of the bit may likewise be readily controlled bythe use of conventional surface apparatus.

During the operation of the drill in a drilling sequence, drillingfluid-preferably drilling mud, air, or the likeis passed down throughthe well pipe and thence through the passageway 28 to the jet 30 and thepassageways 33 in the various cutter elements. The drilling fluid aidsmaterially in the drilling operationas in conventional operations ofthis type--by removing cuttings from the borehole, lubricating the bit,etc.

When a. drilling operation is interrupted and it is desired to remove adrill bit from a borehole, the following sequence of operations isemployed. First, the drill pipe and the drive sub 10 are lifted from thebottom of the borehole; and rotation of the equipment is stopped. A toolsuch as that shown in Figure 8 (with pin removed) is then loweredthrough the pipe and the drive sub until the inner conical surface ofthe tool engages theupper ends of latches 19 and forces them together soas to disengage them from the drive sub. An upward pull on the tool thencauses the upper surface of the spearhead 74 to engage the shoulders 61of the dogs 19, with the initial result that the packer 18 is released.

Continued upward pull of the tool lifts the mandrel 11. As a furtherresult, the bit elements 12 are retracted from their drilling positionand lifted Within the drive sub in a sequence which is substantiallyopposite to or the reverse of the sequence by which they were expandedinto drilling position. Thus, the right-hand bit element in Figure 2 isthe first of the cutters to be retracted and withdrawn; and theleft-hand cutter then follows.

Concurrently with retraction of the bit elements, up ward pull of themandrel 11 causes the latch assemblies to be sequentially engaged andlifted with respect to the drive sub. As the grooves 40 in mandrel 11move upward, their lower shoulders engage latch assembly 41. The dogs 14are retracted from the groove or recess 15, and they then enter therecesses 46 and 47 in the mandrel; When this occurs, the drill is in afully retracted position and may be lifted to the surface of the earth.

As mentioned earlier in this description, it is a particularcharacteristic of the drill of this invention that it may drill eventhough it may not be in a completely expanded drilling position. Thisfeature or characteristic of the invention is shown particularly well inFigure 7. Referring to that figure, the bit elements 12 are depictedthere as they would appear in attempting to expand within an under-sizedhole. The bit is capable of being ro- -tated in the hole, but it cannotexpand to its full drilling diameter. It will be noted, however, thatcompensating factors within the apparatus are operative in the figure togradually expand the bit into the fully expanded condition. Thus, thesleeve valve 27 is resting on the lower .shoulder of the valve guideportion 36 of the mandrel;

and the valve ports 32 are therefore out of alignment with the branchpassageways 31. It will be apparent, then, that drilling fluid inpassing down through central passageway 28 is unable to follow its usualcourse through the bit elements 12. Instead, it must travel entirelythrough the jet 30, with the result that an extraordinary amount ofhydraulic force is exerted on the mandrel so as to urge it verticallydownward. There is, therefore,

a continuous effort on the part of the over-all drilling ssytem to urgethe bit elements 12 into their expanded position; and this effort iscontinuous until this objective is realized.

Also of particular interest in Figure 7 is the fact that the matingcurved spline portions of the cutter elements and the drive sub enablethe cutter elements to articulate relative to the drive sub during theentire time that the mandrel 11 is urging them into an expandedposition. This feature is an especially desirable one in that the bitcan be expanded in a hole smaller than one the nominal gage of the bit.Such holes are frequently encountered as a result of wear of the outerdiamonds of the preceding bit. Thus, the borehole is quickly restored toits nominal gage, providing for easy insertion of a large size of oilwell casing after the well is drilled.

The foregoing description has been limited to an apparatus which iscontemplated to be the best mode of practicing the invention. However,it will be recognized that numerous variations and modifications arepossible without departing from the spirit or scope of the invention.For example, it is contemplated that the center mandrel need not alwayshave an abrasive cutting surface as where the drill is used for reamingpurposes.

The invention claimed is:

1; In a retractable and expansible drill including a mandrel, aplurality of bit elements movably supported from the mandrel by means ofelongated support members, and a tubular member adapted to receive themandrel and the bit elements in a manner to assemble the bit elementsadjacent one end of the tubular member after passage therethrough, saidmandrel being adapted further to move longitudinally relative to theassembled bit elements and to wedge said bit elements against thetubular element, the improvement which comprises an abrasive-typecutting surface covering each bit element and the wedge-end portion ofthe mandrel, said mandrel being coextensive with said bit elements whencompletely wedged and expanded so as to integrate the various cuttingsurfaces, positive-type mating means on each bit element and saidtubular member to resist lateral peripheral movement between theexpanded bit elements and the tubular member, a central fluid passagewayextending longitudinally throughout said mandrel, a separate branchfluid passageway intersecting said central fluid passageway andextending toward each bit element, a separate fluid passageway extendingthrough each bit element, and valve means on said mandrel adapted tointerconnect each branch passageway with a bit passageway when the bitelements are fully expanded.

2. An apparatus as defined in claim 1 in which the valve means is asleeve valve movable along the mandrel.

3. In a retractable and expansible drill including a tubular subattachable to the lower end of a string of drill pipe, a mandrelinsertable into the sub from the drill pipe, a plurality of bit cutterelements, a separate support member connected to each bit element and inturn supported in a longitudinally movable relation by the mandrel, saidsu-b upon insertion of said mandrel being cooperable therewith toassemble said cutter elements ad- 'jacent the lower end of the sub, apacker supported around said mandrel and operable to seal the annularspace between the mandrel and the sub, said mandrel upon assembly ofsaid cutter elements being adapted to wedge said cutter elements againstsaid sub, the improvement which comprises an abrasive cutting surface onthe lower end of said mandrel and on the lower and outer surfaces ofeach cutter element, all lower cutting surfaces defining a coextensiveintegral cutting surface upon complete expansion of the cutter elements,positive-type in- -terengaging means on each cutter element and said subI to resist rotational movement between said cutter elements and saidsub, each cutter element being pivotally connected to its respectivesupport member, said interengaging means defining a curved bearingsection to facilitate expansion and retraction of said cutter elements,a main fluid passageway extending throughout the length of said mandrel,a separate fluid passageway in each cutter element, and normally closedvalve means on said mandrel operable upon complete expansion of thecutter 12 elements to. interconnect the main passageway with the cutterelement passageways. r 4. An apparatus as defined in claim 3 in whichthe abrasive cutting surfaces are diamond surfaces.

'5. An apparatus as defined in claim 3 in which the interengaging meansare mating longitudinally disposed splines on each cutter element andsaid sub.

6. A retractable drill comprising a conduit-like elongated drive subattachable to the lower end of a string of well pipe, an elongatedmandrel lowerable within said sub, a plurality of bit element supportsspaced around said mandrel, each support being retractably mounted atits upper end to said mandrel and terminating at its lower end belowsaid mandrel, an abrasive-type bit ele ment pivotally attached to thelower end of each cutter support, a plurality of longitudinally disposedsplines spaced around the inner periphery of and near the lower end ofsaid sub, each bit element having a splined outer portion adapted toengage the said sub splines, said bit element splines and said subsplines having rounded matching profiles to enable said cutters to pivotwithin saidsub, means'associated with said sub to retract the upper endof said cutter supports from said mandrel when said cutter splines andsaid sub splines are in lateral alignment thereby enabling said mandrelto move downward relative to said cutters, the lower end of said mandrelterminating in .an abrasive cutting surface and adapted to urge said bitelements outward thereby engaging said bit element splines with said subsplines, retractable interengaging means between said mandrel and saidsub to lock said mandrel within said sub, lost-motion means between saidretractable latching means and said mandrel to enable limitedlongitudinal movement between said mandrel and said sub, a packermounted exteriorly of said mandrel and adapted to effect a fluidtightseal between said mandrel and said sub, a central drilling fluidpassageway extending throughout the length of said mandrel, drillingfluid passageways in said bit elements, and branch drilling fluidpassageways in said mandrel interconnecting said central passageway andsaid bit element passageways when the lower surfaces of all abrasivecutter elements are laterally flush with one another.

.7. A retractable drill comprising a tubular sub adapted to be attachedto the lower end of a string of drill pipe, a mandrel adapted to belowered within said sub, a plurality of bit element supports spacedaround said mandrel, the upper end of each bit element supporttermimating in a dog retractably mounted within said mandrel,

the lower end of each bit element support terminating in a diamond-typebit element depending below said mandrel, a plurality of verticallydisposed splines extending around the inner surface of said sub near thelower end thereof, a splined outer portion on each bit element adaptedto engage the splines of said sub after the cutting surfaces of the bitelements have passed through said sub, the splined portion of each bitelement and the splines of said sub having a rounded profile to enable apivotal-type motion of said bit elements relative to said sub, meanswithin said sub adapted to retract and receive said dogs from saidmandrel substan tially concurrently with the engagement of said bitelement splines and said sub splines, the lower end of said mandrelterminating in a diamond cutting surface and shaped to urge said bitelements radially outward from said mandrel so as to engage said bitelement splines and said sub splines, combination lost-motion means andretractable latching means to retain said mandrel within said sub, acentral drilling fluid passageway extending throughout the length ofsaid mandrel, at least one drilling fluid passageway in each said bitelement, a plurality of branch drilling fluid passageways in saidmandrel interconnecting said central passageway with said bit elementpassageways when the lower surfaces of said mandrel and each bit elementare laterally flush with one an- 13 other, and a packer on the outersurface of said mandrel adapted to seal the annular space between saidmandrel and said sub.

8. In a retractable and expansible drill including a mandrel carrying aplurality of bit elements and a tubular member adapted to receive themandrel and bit elements and cooperable therewith to expand the bitelements at one end of the tubular member after passage therethrough,the improvement which comprises means to wedge said mandrel between theexpanded bit elements and to urge the bit elements into contact with thetubular member, interengaging means provided upon contacting portions ofeach bit element and said tubular member to resist rotational movementtherebetween, an abrasive cutting surface on each bit element,contacting portions of each bit element and said tubular member beingshaped to define curved bearing surfaces to enable the bit element topivot relative to said tubular member upon expansion and retraction ofthe drill.

9. In a retractable and expansible drill of the type described includinga tubular member adapted to be attached at its upper end to the lowerend of a string of drill pipe, a mandrel and a plurality ofabrasive-type bit elements dependent therefrom adapted to be loweredwithin the sub and cooperable therewith to expand the bit elements intoa positive-type engagement against the lower end of said tubular member,the improvement which comprises fluid passageways in each bit elementand said mandrel for the flow of drilling fluid therethrough, thepassageways in said bit elments being alignable with passageways, insaid mandrel when the drill is in an expanded position, means torestrict the discharge of drilling fluid from passageways in saidmandrel except when said drill is in an expanded position, contactingportions of said bit elements and said tubular member being shaped todefine an arcuate race joint enabling the bit elements to pivot relativeto the tubular member upon expansion and retraction of said drill.

10. In a retractable and expansible drill including a mandrel, aplurality of bit elements movably supported from the mandrel by means ofelongated support members, and a tubular member adapted to receive themandrel and the bit elements in a manner to assemble the bit elementsadjacent one end of the tubular member after passage therethrough, saidmandrel being adapted further to move longitudinally relative to theassembled bit elements and to wedge the elements laterally against thetubular element, the improvement which comprises an abrasive-typecutting surface on each bit element 14 and on the end portion of saidmandrel, said mandrel end portion being coextensive with said bitelements when wedged together so as to integrate the various cuttingsurfaces, positive-type pivotal interengaging means associated with saidbit elements and said tubular member, the end of said tubular member andsaid bit element being shaped so as to define mating curved bearingsurfaces to permit pivotal expansion and retraction of said bit elementsand of a character to resist lateral movement between the wedged bitelements and the tubular member.

11. An apparatus as defined in claim 10 in which said positive-typepivotal interengaging means comprises mating splines on said bitelements and said tubular member.

12. In a retractable and expansible drill including a tubular memberattachable to the lower end of a string of drill pipe, a mandrellongitudinally insertable into said tubular member from said drillstring, a plurality of bit elements suspended from the mandrel by meansof sep arate support members which are movable along the mandrel, saidtubular member being cooperable with said mandrel and said bit elementsand said support members to retractably assemble the elements adjacentthe lowerend of the tubular member, said mandrel being adapted to wedgethe bit elements against said lower end of said tubular member, theimprovement which comprises an abrasive cutting surface on each bitelement and on the lower end of said mandrel, said mandrel in itswedging action being adapted to render its cutting surface coextensiv-ewith the cutting surfaces of the bit elements, interengaging pivotalmeans associated with each bit element and said tubular member, saidinterengaging pivotal means including mating arcuate splines on each bitelement and on said tubular member to permit pivotal expansion andretraction of said bit elements and of a character to resist lateralperipheral movement betweenthe wedge bit elements and the tubularmember. a

References Cited in the file of this patent UNITED STATES PATENTS1,996,132 Walker Apr. 2, 1935 2,099,859 Macready Nov. 23, 1937 2,208,457Hurley July 16, 1940 2,360,088 Walker Oct. 10, 1944 2,545,037 KammererMar. 13, 1951 2,755,071 Kammerer July 17, 1956 2,764,388 Camp 'Sept.25,1956

